Jordi Alba’s 61st minute goal for Barcelona in Saturday’s clash against Celta Vigo was the result of an egregious offside error from the assistant referee.

Though there’s little excuse for missing an offside that the entire stadium could see, the missed call is yet another reminder that the assistant referees have a critical but enormously difficult job, and that an error can change the course of a game. Luckily, there is a way to make that job much easier.

Before you judge too harshly the assistant who missed Alba’s offside and gifted Barcelona their third goal, consider the complex perceptual feat involved in calling offsides. In order to judge it with one hundred percent accuracy, a person would have to focus his attention on the ball, the attacker to whom a pass is aimed, and the second-to-last defender, all in the exact moment that a pass is made.

It turns out that people simply can’t track three objects at the same time, especially three objects that are so far apart. Vision scientists have known for some time that we can only focus our gaze with any real clarity on a small slice of the visual field at any single moment (a circle about five degrees in diameter), and thus our eyes are constantly shifting back and forth without our intent or notice.

When a player makes a pass, the assistant has to quickly shift his gaze from the ball to the last line of defense in order to judge if an attacking player was in an offside position when the ball was played. But in the time his attention shifts, of course, the positions of the players may have changed considerably. The assistant’s task necessarily requires a bit of guesswork and inference.

As a result, assistant referees make errors. Lots of them.

A study of all the matches of the 2002 World Cup found an error rate in excess of 25 percent. In addition, more than five out of six errors benefited the defending teams. Why? One reason is an illusion called the “flash-lag effect,” but the other is more pernicious: offside errors are more visible, and more highly publicized, when they result in goals, so mistakes that lead to goals like Alba’s can be quite damaging to an assistant’s career.

But most mistakes made in favor of defensive teams are whistled before a goal can be scored, so they’re easier for fans and the media to forgive and forget.

Which is why you won’t read about the two missed offside calls in the first half of the Barcelona game, in the 11th and 31st minutes. In each instance, David Villa was played in on the left side of the penalty area and wrongly flagged for offside. In the second instance, he made a pass to an onrushing Messi, who was just about to meet the ball close to the penalty spot when the whistle was blown. Who knows how those particular instances would have turned out?

Messi, after all, was having an off day. But with the sheer regularity of missed calls, one thing’s for sure: we’re missing goals, beautiful goals, as a result.

So what to do? Some say we must resort to replay technology if we want better offside enforcement. But unlike goal-line technology, it’s not at all clear how offside technology would work in practice. Surely, the referees can’t allow play to continue until someone in a booth somewhere carefully replays the tape and makes the judgment. But just as surely the referee can’t stop the play every time there is a suspected offside offence, as there would be no way to reset the play if it turned out there had been no offside after all.

A simpler—but by no means foolproof—solution (via @Eluberoff) is to eliminate the need for the assistant referees to track the ball at all. Instead, they would hear a beep in their earpiece, courtesy of a new fifth official clicking a button with every pass—or even every touch—by an attacking player.

In that scenario, the assistant would merely have to judge the position of the attacking player relative to the last defender with each beep, and see whether he subsequently receives or pursues the ball before the next beep arrives.

Perfect? By no means. But surely with so many game-changing calls on the line, some experimentation is called for. Otherwise, we’ll see more goals like Jordi Alba’s, and we’ll miss out on countless more.